2nd-3rd Grade

Associated Videos:

Bill Nye – Atmospheric Pressure

History of Barometer (TED-ED video)

Pressure Activity 1

This activity can be downloaded here

Overview

To show that air has weight, the air is removed from one of two balanced balloons throwing the balance off.

TOTAL TIME 10 minutes.
SUPPLIES Yard/meter stick; two large balloons; string; transparent adhesive or masking tape
PRINTED/AV MATERIAL None
TEACHER PREPARATION You can have someone hold the string (attached to a year/meter stick) or you may want to have a piece of string hanging from the ceiling before class.
SAFETY FOCUS Severe thunderstorm safety

The number of molecules in the atmosphere decreases with height.

The atoms and molecules that make up the various layers in the atmosphere are constantly moving in random directions. Despite their tiny size, when they strike a surface they exert a force on that surface in what we observe as pressure.

Each molecule is too small to feel and only exerts a tiny bit of force. However, when we sum the total forces from the large number of molecules that strike a surface each moment, then the total observed pressure can be considerable.

Air pressure can be increased (or decreased) one of two ways. First, simply adding molecules to any particular container will increase the pressure. A larger number of molecules in any particular container will increase the number of collisions with the container’s boundary which is observed as an increase in pressure.

A good example of this is adding (or subtracting) air in an automobile tire. By adding air, the number of molecules increases as well a the total number of the collisions with the tire’s inner boundary. The increased number of collisions forces the tire’s pressure increase to expand in size.

The second way of increasing (or decreasing) is by the addition (or subtraction) of heat. Adding heat to any particular container can transfer energy to air molecules. The molecules, therefore, move with increased velocity striking the container’s boundary with greater force and is observed as an increase in pressure.

Procedure

    1. Inflate two balloons so they are the same size.
    2. Tape one balloon to each end of the yard/meter stick.
    3. Tie a string to the center of the stick and adjust it so the stick balances when held by the string. Tape the string in place to prevent it from slipping.
    4. Ask the students, “If one end were heavier, would the heavier end move up or down?”
    5. Carefully deflate the other balloon. Try poking the balloon with a pin in its neck to prevent the balloon from tearing apart as it pops.
    6. Let both balloons hag freely on the yard/meter stick. Ask the students to explain what happens to the balance.

Discussion

Air is all around us. This air is composed of atoms and molecules. Despite their small size, the number of atoms and molecules exert weight on us known as pressure. Since our bodies are designed to live in this environment, we do not notice the pressure.

Since the inflated balloon now weighs more than the deflated one (due to the air inside of the balloon) it will sink creating an imbalance. Now, imagine the weight of air if that balloon were now 15 miles (24 km) tall.

That is actually what is occurring at this moment in your classroom. When we measure air pressure with a barometer, we are measuring the weight of a column of air 15 miles (24 km) high directly over us.

Live Weatherwise

The weight of molecules also affects the weather. One measure of the severity of a thunderstorm is the wind speed. In addition to the size of hail, the National Weather Service defines a severe thunderstorm as one containing wind speed of 58 mph (50 kts / 93 km/h) or greater.

The weight of all of the molecules in wind of 58 mph (50 kts / 93 km/h) is the force that can create hazardous weather conditions such as blowing down phone and power lines, trees, and make driving hazardous. When the National Weather Service issues a Severe Thunderstorm Warning it means thunderstorms with wind gusts to 58 mph (50 kts / 93 km/h) or greater and/or hail size of 1″ (2.5 cm) or greater is occur or about to occur near you.

Discuss severe thunderstorms with your family. Everyone should know what to do in case all family members are not together. Preparing for a disaster ahead of time helps reduce fear and lets everyone know how to respond to a severe thunderstorm.

Take an American Red Cross first aid and CPR course to learn how to treat burns and how to give rescue breathing and administer CPR. Everyone should know how to respond because severe weather can strike almost anywhere in the country.

Postpone outdoor activities if thunderstorms are likely. Many take shelter from the rain, but most who are struck by lightning are not in the rain! Postponing activities is your best way to avoid being caught in a dangerous situation.

Fast Facts

  • Baseballs travel farther in moist air than in dry air. For any given volume of air, moist air (at the same temperature and pressure) has exactly the same number of molecules as dry air.
  • Dry air is composed of mostly of heavy oxygen (O2) and nitrogen (N2) molecules. However, in moist air, some molecules are the lighter weight water molecules (H2O), rather than heavier O2 or N2 molecules.
  • Therefore, the air is less dense in moist air and this decrease in density equates to less resistance to the ball’s motion through the air. So, for two baseballs hit with equal force, the one in the moist air would travel farther than the one hit in the dry air.

Source: National Weather Service and National Oceanic and Atmospheric Association

Pressure Activity 2

This activity can be downloaded here

Overview

We typically do not “feel” atmospheric air pressure. Why? Since air surrounds our bodies, and all things, the pressure, as a result of the air, is applied equally on all sides. For example, if someone holds an 8½”x11″ sheet of paper by their hand at arm’s length, the weight of the air directly above the sheet is over 1,300 pounds.
Obviously, the paper does not weight that much. Why? That same pressure (14.7 pounds per square inch) is also pressing up on the bottom side of the paper. The equal pressure on all sides cancels each other out so all that is left is the weight of the material that comprises the paper. Since we do not normally “feel” air pressure, the student will see how the effect of the air pressure on two sheets of paper.

TOTAL TIME 2 minutes
SUPPLIES Ruler; a sheet of printer paper; newspaper
PRINTED/AV MATERIAL None
TEACHER PREPARATION None
SAFETY FOCUS Thunderstorm safety

Procedure

  1. Lay a ruler on a table with about 3″ (8 cm) hanging over the edge.
  2. Lay a sheet of printer paper on the part of the ruler in direct contact with the table.
  3. Press the paper against the table until it is flat as possible.
  4. Press down on part of the ruler hanging over the edge.
  5. Repeat the above steps except replace the printer paper with a large sheet of opened newspaper in the second step.

Discussion

The student will discover the newspaper was much harder to lift than the printer paper. As the ruler lifted the printer paper, air rush in under the rising paper and thereby quickly allowed the air pressure to equalize on all sides. Essentially, the weight of the air above the paper had no effect on the difficulty in lifting the paper.

As the ruler lifted the newspaper, the edges of the newspaper remained in contact with the desk. Very little air was allowed to rush in and equalize the pressure on the bottom side of the newspaper. Since there is less air below the paper the pressure is less as well. Now the weight of all the air above the paper now becomes more evident.

Source: National Weather Service and National Oceanic and Atmospheric Association

Pressure Activity 3

This activity can be downloaded here

Overview

Pressure is not only a matter of altitude but also is dependent upon the temperature. As the temperature increases so does the pressure. The molecules and atoms that comprise the air we breathe gain energy as they absorb heat. That increase in energy results in faster moving atoms which we observe as an increase in energy.

The opposite occurs when the temperature decreases. As the molecules lose energy, their motion is decreased and we observe a decrease in pressure. The students will see a plastic 2-liter bottle crushed by the normal atmospheric pressure in the room by this decrease in pressure.

TOTAL TIME 10 minutes
SUPPLIES Two empty 2-liter bottles, hot tap water
PRINTED/AV MATERIAL None
TEACHER PREPARATION None
SAFETY FOCUS Tornado safety

Procedure

  1. Place two cups of hot tap water into each two 2-liter bottle.
  2. Place your thumb over each bottle opening and shake. This ensures the air inside the bottle is warmed.
  3. Pour the water out of each bottle and screw a bottle cap on only one of the two bottles.
  4. Stand both bottles side-by-side and observe over the next five minutes.

Discussion

The bottle that was capped will eventually begin to collapse. This is a result of the cooling air inside that bottle. The air cools because the molecules and atoms inside the bottle lose energy as they collide with the bottle side that is exposed to the cooler surrounding air.

As their energy decrease so does their velocity and therefore the pressure decreases. Since the pressure inside the bottle decreases, the force of the air outside the bottle begins to crush the bottle.

However, the uncapped bottle remains unchanged. As the air cools inside, the drier outside air flows in to take up space thereby keeping the pressure the same both inside and outside of the bottle.

Fast Facts

  • We can only swim down to a relatively shallow depth before the increased pressure from the water crushes our bodies. At a certain point, the outward pressure in the lungs exceeds the structural integrity of the rib cage, and the rib cage collapses would kill a human being.
  • As such, the world’s record SCUBA dive is 1090 feet 4½ inches (332.35 meters) set in 2014.
  • However, whales can withstand this pressure because their bodies are more flexible. Their ribs can collapse safely under pressure, which keeps them from rupturing. This allows sperm whales, which dive to depths of 7,000 feet (2,100 meters) or more to hunt for giant squid.

Source: National Weather Service and National Oceanic and Atmospheric Association

Pressure Activity 4 (Weather station activity)

This activity can be downloaded here

First, measure the pressure in your classroom or outside on a clear and sunny day. Keep a watch on your local weather forecast, and when a storm is expected turn on the weather station. The change in pressure occurs too slowly to notice from hour to hour. You can turn it on for only five minutes. Keep track of what time you turn it on. Have the students record the pressure and time in their lab notebooks. The mass of air around your location will decrease as the storm approaches. The students will see the pressure decrease. After the cold front passes your location, higher pressure will move in, and the students will see the pressure increase.

Source: National Weather Service and National Oceanic and Atmospheric Association

Writing Activity

Have the students write a paragraph or two explaining why the pressure changed when it did. Tell them specifically to write about the differences between the low-pressure state and the high-pressure state.

Fast Facts

  • The scientific unit of pressure is the Pascal (Pa) named after Blaise Pascal (1623-1662). One pascal equals 0.01 millibar or 0.00001 bar. Meteorology has used the millibar for air pressure since 1929.
  • When the change to scientific unit occurred in the 1960’s many meteorologists preferred to keep using the magnitude they are used to and use a prefix “hecto” (h), meaning 100.
  • Therefore, 1 hectopascal (hPa) equals 100 Pa which equals 1 millibar. 100,000 Pa equals 1000 hPa which equals 1000 millibars.
  • The end result is although the units we refer to in meteorology may be different, their numerical value remains the same. The standard pressure at sea-level is 1013.25 in both millibars (mb) and hectopascal (hPa).

Spelling/Vocabulary Activity

Download the Word List here